Why is that always the response around here when one can't back up their points otherwise?
Get used to that response.
How is it The Spider-man Sampler is not the first appearance? It came out in may of 2012, months prior to Avenging 9. At the very least it's the first Danvers as Cap cover.
Is it a standalone story, or preview pages?
Introducing The New Captain Marvel right on the cover, this is the cover image to Avenging 9 and the first time we see her in the costume and named as Captain Marvel. Looks to me like this freebie is
first Danvers as Captain Marvel
first costume
first Danvers as Cap Marvel cover.
I really cannot see how anyone here can dispute this.
Looks like your market is already correcting itself, these could be had yesterday for peanuts and even less in large quantity from MCS.
http://www.ebay.com/itm/SUMMER-OF-SPIDERMAN-PREVIEW-RARE-GIVEAWAY-PROMO-2012-PROMOTIONAL-AMAZING-NM-/190689865019?pt=US_Comic_Books&hash=item2c66006d3b
Yup.. Regardless of this whole chicken/egg petty argument, this is indeed, a 3rd key